Electrolytic production of esters



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P. v. HMAN Filed ban. 18, 1938 ouzt ELECTROLYTIC PRODUCTION OF ESTERS Sept. 20, 1938.

NKENUR. /mavz @fair/6? @Av/W A TTORNEY Patented Sept. 20, 1938 A UNITED STAT ELECTOLYTIG PRODUI'ION 0F ESTERS Per vanter maan, Gym

rp, Sweden, assigner `to Nitroglycerin Aktiebolaget, Gyttorp, Sweden, a

registered company Application January 18, 1938, Serial No? 185,623

In Syweden December 10, 1934 201Claims.

actionaof an oxidizingnature upon unsaturated carbon compounds. p 4

Thiszapplication is a continuation-impart of Vmy copending application, Serial Number 51,709 led November 26, 1935. In my acknowledged application I have described the process of electrolytically producing nitric acid esters and I have particularly illustrated the speciflcation by examplesreferringmo the anodic omdation of vunsaturated hydrocarbons containing an oleiinic bond, in the presence of an electrolyte containing nitrate ions. The`A reaction is, however, by no means limited to'such compounds,

the faculty of forming esters at the anode during electrolysis being a property not nonly peculiar to olefinic hydrocarbons, it having been proven by actual tests that unsaturated carbon compounds 20 in general which contain one or` several double bondsof an unsaturated character linking car- ,bon atoms can give rise to nitric acid esters when treated under the appropriate conditions.

The general usefulness of the various vmeans of "producing the most favorable conditions of reaction as outlined in my .above copending application has also been demonstrated in these other cases. Thus a high concentration of the reacting substances in the'anode film or its immediate vicinity should be aimed at and can be attained by mechanical means, e. g. by introducing the carbon compound in the anode chamber through va porous wall against which the anode e. g. in the form of a wire gauze is placed, -as shown in the copending application, or, in the case of a gasecus carbon compound, by'feeding it under pres` sure to' the anode. Again, high concentrations of the carbon compound in the anolyte can be attained by using an anolyte having a high solu- -1 40 bility for the substance to be treated. To the electrolyte/is-suitably added a conducting salt, preferably calcium nitrate. This is particularly useful when the reaction is carried out in a substantially water free medium. Acetic acid and 45 'acetone are suitable as solvents for the sulktances 50 may also be obtained from the anolyte in any V- to be esterifled or as compo'nents of the electrolyte, although other solvents in many lcases may be employed as should be clear with organic chemistry. The formed product )suitable manner, e. g. by salting out, by extraction, by evaporation, etc.

To' further increase the yield of the desired product this should be protected -as much as possi- 55 Y ble against a continued action fromthe reagents,

once it has formed. Thus, a so-called esterification in two-phase system may suitably be applied,

by the introduction into the anode compartment of a solvent for the nitric acid ester, which is im- 60, miscible with or has a low solubility in the anolyte,

for this purpose.

palladium anode will to anybody familiar and which will thus immediately remove the ester from the reacting system as it is formed. When using aqueous solutions, chloroform is suitable Catalysts will yalso in many instances greatly inuence the `reaction. A suitable catalyst should be preferential, i. e. favourably iniluene the velocity of the main reaction while being without influence or even have a depressing action upon side-reactions and on such reactions which would tend 'to destroy an"already formed desired prod; uct. The anode per se, may also serve as such catalyst.

VSince a high oxygen pressure is evidently of favorable inuence upon the reaction, the discharge voltage of oxygen on the anode should be high, i. e. such conditions should be selected which have a depressing eiect upon the evolution'of oxygen at theA anode. This may be obtained by uselecting a suitable anode material, e. g. as above mentioned, smooth platinum, gold, iridium, or alloys thereof, which show a high overvoltage toward oxygen, and also by giving the anolyte a suitable composition and temperature. Another factor to be considered in this connection is the 4current density at the anode surface, as well as the surface condition of the latter.

j The selection of anode material will often depend on the fact, that a certain material, which otherwise would be suitable, may also have such a promoting action on undesired side-reactions that it must be exluded for this reason. Thus a cause side-reactions to such a degree that it is unsuitable in cases where a formation of ethylene nitrate is chiefly desired. Similarly, optimum temperatures and suitable compositions of the anolyte are dependent on factors which may have an iniiuence in various directions. The hydroxyl ion concentration should, however, as a rule be kept low at the anode.

The technical realizationof these reactions require as indicated above, the best possible contact between anode surface. and reacting compounds. The electrolytic cell may thus, in such cases when the carbon compound is in the gaseous state, suitably be builtl as a more or less gastight chamber in which the separated by mealns cfa porous diaphragm. l

An electrolytic cell of this type is illustrated in the accompanying drawing which represents a anolyte and catholyte are vertical section through a cell which is useful in mounted on the outside `lof the gas distributing may be `correspondingly diaphragm 3. as shown.

tube while the cathode 6 mounted on the porous The anolyte d is then placed between the gas distributor and the porousdiaphragm, while the catholyte 'ly is placed in the outer vessel and is separated from the anolyte bythe poro'usdiaphragm. A gaseous unsaturated carbon compound is introduced into the gas distributor 2 by the tube at the top, as shown by the arrow. It passes through the gas distributor into, the anolyte A and the gas which is not absorbed passes out through the tube at the top of the anode compartment, as shown by the arrow.

This arrangementD shown in the drawing has been used in carrying out the esterifications of ethylene referred to` in Example 1 below. Particularly in the case of reactions with carbon compounds in solutionyan arrangement without t fa diaphragm or porous anode wall may also be used. It is e. g. possible to saturateAzhe electro- .lyte outside the electrolytic cell with the carbon 20 compound in question and afterwards introduce this solution in the electrolytic cell. This procedure is, of course, possible to use in the case of both gaseous, liquid, and/solid carbon compounds. The formed product may be obtained from the anolyte in any suitable manner, e. g. by a saltingout, by producing a low solubility in the electrolyte, by extraction (particularly in the case of the above mentioned two-phase reactions), by evaporation of the anolyte, etc.`

As an .example of reactions according to the invention the following may be mentioned:

EXAMPLE 1 Eaterjcaticm of ethylene i :inode: smooth platinum gauze 100x 80 mm., diameter of wire 0.1 mm.,

aimera e f amples by no means conne the invention' to the classes of compounds spe'cically mentioned in the following.

Example 4.-'Iype: Esters containing a. double bond of an unsaturated character, including unsaturated cyclic double bonds, that is, cyclic oletine` esters, halogen esters and esters of organic and inorganic oxygen-acids, etc.

`(a) Vinyl bromide HzCrCHBr. Anolyte consisting of 5 gm. Ca(NO3)2, 5 gm. acetic acid and 90 gm. acetone containing about 1% by weight of vinyl bromide. Nitrogen ccnl tent of product: 6.76%. l

(b) Allyl bromide H2C:CHCH2Br. Anolyte consisting of 10 gm. allyl bromide, 10' gm.

acetone. Nitrogen content of product: 3%. (c) Vinyl acetate H2C:CHOOCCH3. Anolyte: 5 gm. Ca('NOa) 2, 90 gm. acetone containing about 0.3% by weight of vinyl acetate. Rendered acid and mixed with C02. Nitrogen content of product: 9.7%.

Example 5.-Type: Organic acids containing a double bond of an unsaturated character, including olenic cyclic bonds.

(a) Acrylic acid. HzCzCHCOOH. Anolyte: Ni-

tric acid of 20% strength containing abolt 0.3% by weight of acrylicv acid. Nitrogen content of` product: 10.6%.

number of meshes per sq. cm. about 100. y

f" v Content of Potential Current in- Current .szotemetnc Electrolyte Catholyte tensity dgltlff elciency nitrogen in `-product 40 10o s t l P n: I P em 0m. 806 One 670 TC 10 cm waren-- FO" 1 uw 80m' }About 0.2:; 4. o-4. 7v. a 61 V 1a. 34 ogo Ca( NOa )z cm. ace one Y- v, 10 g Camo, L M .-do do 4.1-4.6v. 75 13.14 100 cm.3 acetone 4 5 em.3 HNO; do do 3. 8-4. 1v. 79 ,f 13. 78

0 10(usp. ga. 1.42) v Cm. ace 0119 lo g Camo --ao 1.1-3.1 About aov. c4 t 14.70

Examinar 2 Estejcato'n of bull/Iene Apparatus as in previous example.

Percent Percent 100 cm.a acetone Ca(N0a)s 1n aqueous solu- 10 CMNOa), om }About 0.4L 7.2fsl2v. $1 10.8

i Normal butyiene (Untertanen.) was used in the test.

" Exsnrm 3 Esterijcatlon o'fpropulene Anode ot Piz-gauze as above 05 x' 95 mm. applied en the outside of a porous alundum tube.

o P nu P mit 100 cm.:i acetone Ca(N0a)a in aqueous solu- "c e' 10 g Samos): um About 0.48-. 6.7 1. 5v. aa 11.63

Note: By current eticiency is meant the ob tained quantity of nitric acid esters in per cent of the theoretical maximum yield of dinitrate oi ethylene, butylene, etc. (C2H4 (NO3).2; C4Ha (NO3) 2. etc.) f

The following examples will serve to demonlo strate the Wide scope of` the invention by typifying certain general classes of compounds which may be converted-into nitric acid esters by em ploying the reactions set forth in my above mentioned copending application, but it must at .the same time be understood that these further ex- (b) C rotonic acid (alpha) HaCzCHCHsCOOH. Anolyte: 5 gin. Ca.'(NO3) 2, 90 gm. acetone containing about 0.05% by Weight crotonic acid rendered acid and mix'ed with CO2. Nitrogen content of product: 9.7%.

(c) Maleic acid.

HCCOOH HCCOOH Anolytey: 5 gm. maleic acid, 5 gm. Ca(NOa)a and 50 gm. acetone. Nitrogen content of product: 6.4%.

Ca(NO3)2, 10.gm. acetic acid and 100 gm.'

70 examples given Example 6.-TyperAlcohol's` containing a dou. ble bond of an unsaturated character.

Example 7.-Type; Derivatives of .oleilnichyr l drocarbons andvcontaining more than one double bond of an unsaturated character i. e. poly-ene compounds of aliphatic or cyclic nature also comprising partly halogen substituted compounds.

(a) Isoprene CH2:C(CH:)CH:CH2'. A'nolyte: 5

Ca(NOs)z, 90 gm. acetone containing about 0.5% of isoprene. Stirred with C02. Nitrogen content of product: 5.0%.'

(b) Butadiene. CH2:CHCH:CH2. Anolyte: 042 gni. butadiene dissolved in.100 ccs. liquid, consisting of acetone with by weight Ca(NO3)2 acidied vwith acetic acid. The anode` consisted .oi\ a. rotating platinum i i gallZe.

t r, solved in' sulphuric acid.

J (c) Di-methyl-butadiene CHsCHrCHCHzCHCHa.

4(d)V Allene CHz-:C:CHz. Anolyte: Acetone oon--` taining 10% by weight CaiNOa): and

10% concentrated acetic. Ariodez--Plati-v numfgauge on the outside of a diaphragm, through which the aliene was slowly fed into the analyte. Nitrogen content of prod- (e) Chloroprene H2C:CC1CH:CH2. Polymerized C `chloroprene, so called Duprene was vdepolymerized by dry distillation. 05 gm. of the received product was dissolved in 100 ccs.

anolyte consisting of acetone withy 10% Ailfa(l\1'0s)i. Afr-rotating anode of platinum.

/1 gauze was used. 'Ihe product contained 3.2% of chlorine and exploded when dissolved in concentrated sulphuric acid. The nitrogen content of the product was 1.6% ,N or more.

(i) Phorone (CH3)2C:CHCOCH:C(CH3):. Anolyte: 5 gm. phorone, 10 gm. acetic acid, 10

gm. Ca(NOa)z diluted with agetone to 200 cm3. Nitrogen content in product: 3.5%.- (gl Cyclo-pentadiene o cnzcn /CHa v CHzCH Anolyte: l0 gm Ca(NO:)n, 10 gm. acetic (acid and 180 gm. acetone containing about 0.1% cyclopentadiene. Nitrogen content of product: '1.5% .(product in liquid state) e ,8.4% (Product-solid).

(h)"Pyromucic,acid

. Hczccoon l f w l\ .i ,r V/0 d.

H l u Anoiyt 5 gm. camom. 5 gm, acetic acid. 35 and 9 5 gm.'acetone containing about 0.3%

pyromucic acid. Nitrogen content of prodxuct: 5.6%. l Y, The nitrogen content was. in all cases determined in an azotometerin the usial way. In all' above, the anode consisted of a platinum gauze ing application, serial ,Number 51,709, the selecv tion of the best anode material must be governed by'several considerations. 'Theprocess is thus by' 75 no means restricted to using a platinum anode.

The sample exploded when dis-f nitrate ions.

`saturated organic compound is ethylene. but as described inJ my copendr It has proven of particular advantage to use a catholyte containing as fairly high amount of acetic acid and also suitably containing nitrate ions e. g. as" calcium nitrate, especially in cases where the anolyte contains organic solvents e. g. 6

; acetone. When using a diaphragm, the acetic acid has a cleansing action upon this due to its faculty for keeping such organic bodies, coming from the anode compartmenain solution, which otherwise have a tendency to precipitate when mixed with catholytes containing higher percentages of Water. For this reason it is also advisable, to keep the catholyte in a slow'streaming motion throughthe diaphragm in direction towards the anode compartment.

In order to prevent, as much as possible, a Iormation of undesired .bodies in theV cathode comf c' partment e. g. .by reduction of nitrates, etc. in the' vicinity of the cathode, such conditions near this should beichosen which tend to counteract reduc-,- if@ ing reactions e. g. introduction of oxidizing 1 fagents, such as-air, oxygenr or other suitable chemical bodies near the cathode, as well as selecting a cathode material which serves the same purpose. f if" As should be plain from the numerous examples given, the process also applies to aromatic compounds having unsaturated side 'chains of the same character as stated above.

The nitric acid esters obtained by the anodc oxidation process are particularly usefus asexplosives or admixtures to shock sensitive products used as explosives as already set forth in my above mentioned copending application, Serial Number 51,109.f

As there shown, when aqueous solutions and ethylene are employed in my process, Ivarious side reactions occur resulting in theuformation of polyglycol nitrates, one of which has the formula:

These polyglycol nitrates possess explosive characteristics similar'to those of glycol nitrate, for which reason it is not necessary to separate them from the reaction/products. The same is true of a number of other bodies which are formed in al similar manner by way of side reactions. In the manufacture of the so-called safetyexplosives an admixture of polyglycol nitrate has even been found of direct advantage due to its low sensitivity to shock. Thef reaction products obtained `by my method are less sensitive to shock than pure glycol/nitrate owing tofthe inclusion of these side reaction products. It it should be desired to suppress these side reactions, the reaction medium should, of course, be as free from water as possible.

. I claim:

1. The processi of making nitric acid esters which comprises the step of submitting an unsaturated organic compound, containing at least` one olenic double bond of unsaturated charac ter linking carbon atoms, to anodic oxidation in the presence of ian.A electrolyte containing 2. The process". of claim 1 wherein said un`.

` saturated organic compound is a gaseous hydrocarbon of the olen series. s

3. The process of claim 1 wherein. said un- 4. The process of claiin l wherein said unsaturated organic compound containing at least one olenic double bond is selected from a group of such compounds consisting of organic acids,

ketones, hydro.- 'l5 alcohols.' poly-ene compounds, 3

carbons, halogen'iesters, and esters of organic oxy'- acids and inorganic oxygen-acids.

5. The process of claim y1 wherein said un-v saturated organic compound is chlorcprene.

V5. 6. The process of claim. 1 wherein said un- 9. The process of making nitric acid estersv 15 which comprises introducing an unsaturated organic compound, containing at least one olenic double`bond of unsaturatedcharacter linking carbon atoms, into an aqueous electrolytic bath containing a highly conducting nitrate in solution,

2o passing an electric current through said bath between an anode and a cathode, the anode being of a metal producing high oxygen over-voltages, andl recovering the resulting nitric acid esters from said electrolyte.

10. The process of claim 9 wherein a solvent for said nitric acid esters is added to said bath, said solvent being substantially insoluble in said Ibath, whereby said solventdissolves said nitric acid esters`when formed, said esters being then r 3u recovered from said solvent.

11. As a' new composition of matter. a product containing a dinitrated derivative of a lowmolecular unsaturated carbon compound containing an oleflnic bond, dinitrated poly-com- `35 pounds of said unsaturated carbon compound and 45 containing ethylene nitrate, polyglycol nitrate and other side-reaction products of ethylene.; said composition being less sensitive to shock than pure ethylene nitrate and constituting the reaction products obtained by subjecting ethylene y 5o to anodic oxidizing conditions in the presence of an electrolyte containing nitrate ions.4

13. The process of preparing nitric acid esters which comprisessupplying arfeed of a gaseous,

lower membered, olenic hydrocarbon to anA 55 anode while passing an electric current through an anolyte, containing acetone and nitrate ions, to said anode to establish an oxidizing condition at the interface between saidanode and said.

anolyte.

14. The process'of preparing nitric acid esters which comprises saturating a liquid containing nitrate ions with a gaseous, lower membered, olenic hydrocarbon under pressure andmaintaining said liquid under pressure while'subjecting it to electrolytic oxidizing conditions using an anode which produces high overvoltage toward oxygen centratio'n, said anolyte comprising a componenthaving high solvent power for said hydrocarbon. 16. In the process as set-forth in claim 15 the use of an anolyte comprising acetone and calcium nitrate. y 17. The process of preparing nitric acid esters which comprises an unsaturated olenic hydrocarbon to anodic oxidizing conditions in the presence of an anolyte containing nitrate ions,

conditions near the cathode that the reducing action of this latter is at least partly counteracted. 18.J A. process for electrolytic production of nitric acid esters comprising using in an electrolytic cell a suitable cathode and an anode of a material and surface condition producing high overvoltage toward oxygen in contact with an anolytecontaining ethylene, nitrate ions and a component having high solvent power for ethylene adjusting the acidity of said anolyte so that a low hydroxyl ion concentration is obtained" in the vicinity of said anode, eii'ecting a high `conductivity of said anolyte and a suitable catholyte contained insaid cell substantially byv means of the addition of calcium nitrate thereto, circulating ethylene gas through said anolyte, said anolyte being separated from the catholyte of the cell by means of a suitable membrane; and passing a direct electric current through said cell from anode to cathodewhile maintaining said conditions.

19. The process of claim 9 wherein said anode and said cathode are separated by a porous diaphragm 'and the catholyteis maintained slowly streaming'r through said diaphragm towards said anode'.

20. The process of claim 9 wherein an oxidizing gas is introduced into said bath in the vicinity of said cathode. p

' PER VALT HMAN. 

